Lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic projection apparatus is disclosed in which a liquid supply system provides a liquid between the projection system and the substrate. An active drying station is provided to actively remove the liquid from the substrate W or other objects after immersion of all or part of a surface of the substrate W or other objects.

FIELD

The present invention relates to a lithographic apparatus and a devicemanufacturing method.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, such as a mask, may be used togenerate a circuit pattern corresponding to an individual layer of theIC, and this pattern can be imaged onto a target portion (e.g.comprising part of, one or several dies) on a substrate (e.g. a siliconwafer) that has a layer of radiation-sensitive material (resist). Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through the projection beam in a given direction(the “scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.)

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidsupply system (the substrate generally has a larger surface area thanthe final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication WO 99/49504, hereby incorporated in its entirety byreference. As illustrated in FIGS. 6 and 7, liquid is supplied by atleast one inlet IN onto the substrate, preferably along the direction ofmovement of the substrate relative to the final element, and is removedby at least one outlet OUT after having passed under the projectionsystem. That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 6 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 6 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 7 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement.

Clearly the presence of liquid in the immersion lithographic projectionapparatus raises difficulties not present in conventional lithographicapparatus. For example, sensors such as interferometers for measuringthe position of a substrate table which supports the substrate can beinfluenced by humidity present due to immersion liquid. Furthermore, notall of the solutions described herein for the liquid supply system maybe perfect at containing all of the immersion liquid and some seepage orspillage may occur.

SUMMARY

Accordingly, it would be advantageous, for example, to reduce problemsassociated with the presence of immersion liquid in a lithographicprojection apparatus.

According to an aspect, there is provided a lithographic apparatuscomprising:

-   -   an illumination system adapted to condition a beam of radiation;    -   a support structure configured to hold a patterning device, the        patterning device configured to impart the beam with a pattern        in its cross-section;    -   a substrate table configured to hold a substrate;    -   a projection system adapted to project the patterned beam onto a        target portion of the substrate;    -   a liquid supply system configured to at least partly fill a        space between the projection system and an object on the        substrate table with a liquid; and    -   an active drying station configured to actively remove the        liquid from the object, the substrate table, or both.

Active removal of immersion liquid (which is, in an embodiment,accomplished without substantial heating of the substrate) may ensurethat immersion liquid is in contact with the resist on the substrate (ifthe substrate is the object) for as short a time as possible. This isimportant because the immersion liquid may react with the resist so thatthe quality of the image on the substrate can change according to theamount of time that the resist is in contact with immersion liquid.Furthermore, if an active drying station removes liquid from a sensorthe performance of that sensor may be enhanced. Removing liquid from anobject and/or the substrate table may reduce contamination of theatmosphere in the apparatus with liquid vapor. This may enhance theperformance of any optical sensors which may be present in theapparatus. The active removal generally takes place after the objectand/or substrate table is moved from under the projection system and/orremoved from the liquid supply system i.e. after the supply of liquid tothe object and/or substrate table is stopped.

In an embodiment, the substrate table transports the object to theactive drying station and supports the object during active removal ofliquid from the object by the active drying station. This may ensurethat the active removal of liquid takes place as soon as possible afterremoval from under the projection system (or from the liquid supplysystem) thereby reducing the amount of time that liquid is exposed tothe atmosphere of the apparatus and to the resist on the substrate; thesubstrate does not need to be removed from the substrate table before itis dried.

The active drying station may be positioned between the projectionsystem and a substrate post exposure processing module so that theremoval of liquid can take place between the exposure position and thepost exposure processing module or in the case of a substrate tablemounted sensor, just before measurement using the sensor. That is theactive drying station is within and/or part of the projection apparatusand not the post exposure processing module.

In an embodiment, the drying station comprises gas flow device toprovide a flow of gas over a surface of the object and/or the substratetable. In an embodiment, the gas flow device can provide a flow of gasof at least 50 liters per minute. This may ensure that the humidityinside the lithographic apparatus remains low and can help in keepingthe apparatus stable in terms of temperature fluctuations, for example.The active drying station may comprise a gas inlet configured to providegas onto a surface of the object and/or substrate table and/or a gasoutlet configured to remove gas and/or liquid from the surface of theobject and/or substrate table. In the case of a gas inlet, the gas inletmay comprise a gas knife or a gas shower with at least ten inlets. Bothof those solutions have been found to be particularly effective atremoving liquid from the surface of the object and/or the substratetable.

The active drying station may comprise a spinner configured to spin theobject and/or substrate table. The spinner makes use of centrifugalforces to remove liquid from the object and/or substrate table. Thissolution may be particularly suitable for when the object is thesubstrate in which case the substrate is spun in its major plane aroundits center.

Another alternative which may be used by itself or in addition to any ofthe other measures discussed above, wherein the liquid between theprojection system and an object on the substrate table is a firstliquid, comprises a first liquid dissolving liquid supply deviceconfigured to provide a second liquid, in which the first liquiddissolves, to a surface of the object. In this way the first liquid canbe dissolved in the second liquid. The second liquid itself is chosenfor easy removal from the substrate. This may be effected, for example,by choosing a second liquid which has wetting properties of the surfaceof the object and/or substrate table which promote drying. Alternativelyor additionally, the second liquid may be chosen to be more volatilethan the first liquid such that it easily evaporates off of the surfaceof the object and/or substrate table. In an embodiment, the secondliquid is a ketone or an alcohol.

According to a further aspect, there is provided a device manufacturingmethod comprising:

-   -   providing a liquid between a projection system and an object on        the substrate table;    -   projecting a patterned beam of radiation, through the liquid,        onto a target portion of a substrate using the projection        system; and    -   actively removing the liquid from the object, the substrate        table, or both.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g. having a wavelength in the range of5-20 nm), as well as particle beams, such as ion beams or electronbeams.

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a projection beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the projection beam may not exactly correspond to thedesired pattern in the target portion of the substrate. Generally, thepattern imparted to the projection beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

A patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned. In each example of a patterning device, thesupport structure may be a frame or table, for example, which may befixed or movable as required and which may ensure that the patterningdevice is at a desired position, for example with respect to theprojection system. Any use of the terms “reticle” or “mask” herein maybe considered synonymous with the more general term “patterning device”.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection system, including refractiveoptical systems, reflective optical systems, and catadioptric opticalsystems, as appropriate for example for the exposure radiation beingused, or for other factors such as the use of an immersion fluid or theuse of a vacuum. Any use of the term “projection lens” herein may beconsidered as synonymous with the more general term “projection system”.

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the projection beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 illustrates an embodiment of the active drying station in which agas knife is employed;

FIG. 3 illustrates an embodiment of the active drying station in which agas shower is employed;

FIG. 4 illustrates schematically the principle of a spinner used in anembodiment of the active drying station;

FIG. 5 illustrates, in cross-section, an exemplary embodiment of a gasknife;

FIG. 6 shows, in cross-section, a liquid supply system in accordancewith the present invention;

FIG. 7 shows, in plan, the liquid supply system of FIG. 6; and

FIG. 8 depicts a liquid supply system according to an embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to aparticular embodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL for providing a        projection beam PB of radiation (e.g. UV radiation).    -   a first support structure (e.g. a mask table) MT for supporting        a patterning device (e.g. a mask) MA and connected to a first        positioner for accurately positioning the patterning device with        respect to item PL;    -   a substrate table (e.g. a wafer table) WT for holding a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner for accurately positioning the substrate with        respect to item PL; and    -   a projection system (e.g. a refractive projection lens) PL for        imaging a pattern imparted to the projection beam PB by        patterning device MA onto a target portion C (e.g. comprising        one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation sourceSO. The source and the lithographic apparatus may be separate entities,for example when the source is an excimer laser. In such cases, thesource is not considered to form part of the lithographic apparatus andthe radiation beam is passed from the source SO to the illuminator ILwith the aid of a beam delivery system BD comprising for examplesuitable directing mirrors and/or a beam expander. In other cases thesource may be integral part of the apparatus, for example when thesource is a mercury lamp. The source SO and the illuminator IL, togetherwith the beam delivery system BD if required, may be referred to as aradiation system.

The illuminator IL may comprise adjusting means AM for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator ILgenerally comprises various other components, such as an integrator INand a condenser CO. The illuminator provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross-section.

The projection beam PB is incident on the mask MA, which is held on themask table MT. Having traversed the mask MA, the projection beam PBpasses through the lens PL, which focuses the beam onto a target portionC of the substrate W. With the aid of the second positioner PW andposition sensor IF (e.g. an interferometric device), the substrate tableWT can be moved accurately, e.g. so as to position different targetportions C in the path of the beam PB. Similarly, the first positionerand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the beam PB, e.g. after mechanical retrieval from a mask library, orduring a scan. In general, movement of the object tables MT and WT willbe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst and/or second positioners. However, in the case of a stepper (asopposed to a scanner) the mask table MT may be connected to a shortstroke actuator only, or may be fixed. Mask MA and substrate W may bealigned using mask alignment marks M1, M2 and substrate alignment marksP1, P2.

The depicted apparatus can be used in the following preferred modes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theprojection beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT is determined by the (de−) magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the projection beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizes aprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

According to an embodiment, the lithographic apparatus is provided withat least one active drying station ADS. In an embodiment, the activedrying station ADS is positioned as close as possible to the projectionsystem PL and the liquid supply system LSS which is positioned under theprojection system PL. By active drying it is meant that positivemeasures are taken to remove liquid from an object rather than justperforming normal operations on the object during which liquid mayevaporate or run off naturally and not applying any measures to theobject with the specific aim of drying the object. The liquid supplysystem LSS may be of any type including a localized area liquid supplysystem which provides liquid to a localized area on a surface of thesubstrate as well as to baths in which the whole of the substrate isimmersed, etc.

When the substrate W is first moved from under the projection system PLaway from the liquid supply system LSS (for example when it is liftedout of a liquid supply system in the form of a bath or when water isdrained from that bath) the substrate is taken to the active dryingstation ADS. At the active drying station ADS immersion liquid whichremains on the substrate W is actively removed by one or a combinationof the measures described below. The resist (radiation sensitive coatingon the substrate) is not affected or removed by the active dryingstation ADS.

Although the active drying station ADS will be described in relation toremoving liquid from the substrate W, the active drying station may alsobe used for removing immersion liquid from sensors (which may bepositioned on the substrate table WT and whose performance will beenhanced by removal of liquid) as well as from the substrate tableitself. It may be used to remove liquid from other objects too. In thecase of sensors, the liquid can be advantageously removed prior tomeasurement i.e. before exposure of the substrate W.

After having immersion liquid supplied to the substrate W, it is rarelypossible to remove all remaining immersion liquid from the surface ofthe substrate before processing. Unfortunately immersion liquid candissolve into resist on the substrate as well as the resist dissolvinginto the immersion liquid. Therefore, it is desirable, with the aim ofuniform development of the substrate, to remove the remaining immersionliquid as soon as possible. This is done in the active drying stationADS. The active drying station ADS is, in an embodiment, positioned suchthat the substrate can be dried within a predetermined time afterexposure of the substrate. The predetermined time is, in one or moreimplementations, less than 5 seconds, less than 2 seconds or less than 1second. Furthermore, it is disadvantageous for the humidity in theapparatus to be high so that it is advantageous to remove immersionliquid remaining on the substrate table and sensors etc. as soon aspossible as well. All of these functions can be performed by the activedrying station ADS, in an embodiment, positioned in and/or part of thelithographic projection apparatus. Removal of remaining liquid from thesensors means that liquid cannot disturb proper leveling of thesubsequent substrate, which may be a problem.

Although not depicted in FIG. 1, the active drying station ADS may beprovided with a baffle or other suitable means to fully enclose theobject as it is being dried. For example, the whole of the top surfaceof the substrate table WT may be enclosed with a curtain or baffle inthe active drying station ADS to substantially prevent the spread ofimmersion liquid around the apparatus. A tray could be used to catch anydrips.

Although the active drying station ADS has been illustrated in FIG. 1 asbeing part of the lithographic apparatus, this is not necessarily thecase, and the active drying station ADS may be positioned anywherebetween the position at which the substrate W is exposed to theprojection beam PB and before a substrate post exposure processingmodule at which various processing steps such as baking of the resist,development and/or etching are performed. The active drying station maytherefore be external of the lithographic projection apparatus.

The active drying station ADS can make use of any means to remove liquidfrom the substrate W. In an embodiment, the drying is achieved withoutsubstantial heating of the substrate W as this could unbalance theapparatus due to the generation of thermal gradients. Several examplesof the way in and devices by which the active drying station ADS removesliquid from the substrate W are described below. These methods and/ordevices may be used singly or in combination, either at the same time orone after another, as is appropriate.

In an embodiment, the active drying station ADS is positioned within thelithographic projection apparatus and the substrate table WT transportsthe substrate (or other object) which is to be dried to the activedrying station ADS and supports the object (e.g., substrate, sensor,etc.) during active removal of immersion liquid from the object by theactive drying station ADS. There may be a plurality of active dryingstations, for example, one for the substrate W and one for the sensor(s)on the substrate table WT.

In its simplest form, the active drying station ADS comprises a gas flowdevice 10 to provide a flow of gas over the surface of the substrate W.The higher the flow of gas the more effective and quick is the removalof immersion liquid from the substrate W. In an embodiment, a flow rateof gas of at least 50 liters per minute, in an implementation, at least100 liters per minute is achievable. In an embodiment, the gas isfiltered and/or dried prior to being provided onto the substrate W toavoid contamination of the surface of the substrate W if this iscompatible with the resist (which is not the case for some resists usedfor 248 nm radiation).

In the embodiment illustrated in FIG. 2, the gas flow device comprisesan inlet 50 and an outlet 60. Gas under pressure is provided throughinlet 50 and removed by an under pressure in outlet 60. The arrangementillustrated in FIG. 2 is a so-called gas knife in which the inlet 50 isa nozzle which accelerates the gas towards the substrate W so that itimpinges on the substrate at both a high flow rate and a high velocity.In an embodiment, the gas jet impinges on the substrate at an acuteangle to the substrate W in a direction towards the outlet 60. Such anarrangement is particularly effective at removing liquid from thesurface of the substrate W. The gas flow device 10 may comprise only asingle inlet 50 or a single outlet 60 or may comprise a plurality of inand outlets 50, 60. The substrate W may be moved under stationary in andoutlet(s) 50, 60 as indicated by arrow 15. The in and outlets 50, 60 mayalso be a continuous groove as well as discrete in and outlet ports. Thein and outlets 50, 60 may also be moveable.

It is also possible for the gas flow device only to comprise an outlet60 which is connected to an under pressure. In this case gas as well asimmersion liquid on top of the substrate W will be sucked up through theoutlet 60.

A further embodiment is illustrated in FIG. 3 in which the gas flowdevice 10 comprises a plurality of inlets 50 and no outlets above thesubstrate (although outlets may need to be provided elsewhere to drainoff the excess gas). This is a so-called shower head. In an embodiment,the shower head comprises at least ten inlets 50. The shower head may beof a cross-sectional area which is large enough to cover the whole orpart of the surface of the substrate W. The substrate W may be movedunder the shower head 10 as it dries.

In an embodiment, the active drying station ADS is dimensioned to be aslong as the substrate table WT so that all objects on the substratetable WT (including the substrate and sensor(s)) can be dried at onetime.

Again, in an implementation, filtered gas is used in the shower head 60.

A particularly effective form of gas knife for removing liquid from thesubstrate W or sensor(s) is shown in FIG. 5. The immersion liquid 5 issucked up a central passage 110 which is connected to an under pressure.The passage 110 is, in an embodiment, in the form of a slot (extendingin and out of the page). Gas is supplied from an outer passage 120 oneither, some or all sides of the central passage. The outer passage 120may also be one or more slots. The outer passage 120 may a singlepassage that peripherally extends around the central passage 110. Thus,there is a gas flow over the surface of the substrate W which helps drawgas and immersion liquid 5 up into central passage 110. The outerpassage may be directed at its outlet at an angle to the surface of thesubstrate away from perpendicular and towards the inlet of the centralpassage 110. The bottom surface of the gas knife in which outlet(s) andinlet(s) of the passages 110, 120 are formed may be contoured so thatgas flow from the outer passage 120 to the central passage 110 is smoothe.g. by rounding off the edges (i.e. giving a radius to the edges) ofthe inlet to the central passage 110 and optionally the outlet(s) of theouter passage 120.

In an embodiment, the active drying station ADS is positioned and thepath of the substrate table WT chosen such that the substrate table WTmoves under the active drying station ADS during the substrate table'snormal movement after or before exposure (i.e. no deviation of path waymay be required). Thus, through put penalty is minimized.

A further system which may be used in the active drying station ADS is aspinner which is used for spinning the substrate W in the plane of thesubstrate W around its central point. When the substrate W is spinning(as is illustrated in FIG. 4) centrifugal forces act on the liquid onthe surface of the substrate W which is flung outwards where theimmersion liquid may be collected.

In an embodiment, the active drying station ADS comprises a liquidretrieval device to recover immersion fluid removed from the objectbeing dried. This is particularly advantageous if the immersion liquidis not water.

In a further embodiment which can be used in combination with any one ofthe foregoing embodiments, by being positioned before or after theforegoing embodiments, is to use a drying liquid in which the immersionliquid dissolves on the surface of the substrate W. If the drying liquidin which the immersion liquid dissolves is of a type more easily removedfrom the surface of the substrate than the immersion liquid, this mayspeed up the drying process. Furthermore, by dissolving the immersionliquid, it may be possible to reduce dissolution of the resist ordiffusion into the resist by careful choice of the drying liquid whichis used. Thus, an immersion liquid dissolving liquid supply device isprovided which can provide drying liquid, in which the immersion liquiddissolves, to the surface of the substrate W. The drying liquid chosenfor this task is, in an implementation, more volatile than the immersionliquid such that it can be removed (i.e. evaporated) more easily thanthe immersion liquid. Alternatively or additionally the liquid may bechosen such that it has a high contact angle with the substrate W sothat it beads more easily than the immersion liquid on the substrate Wand can therefore be removed. Suitable liquids are ketones or alcohols,in particular IPA (isopropylalchohol).

It will be appreciated that the present invention has been described inrelation to the substrate W being dried by the active drying station ADSwhile in position on the substrate table WT. This is not necessarily thecase and other objects such as the substrate table WT itself or sensorson the substrate table WT may be dried by the active drying station.Drying of a sensor on the substrate which may be immersed in animmersion liquid on a surface of the sensor (by accident or forillumination, for example) is advantageous. The performance of thesensors is improved by elimination of liquid during measurements and/orelimination of drying marks. Furthermore, it may be necessary to removethe substrate W from the substrate table WT before being dried by theactive drying station ADS, which as stated above, may be positionedoutside of the lithographic apparatus. Indeed, even if the active dryingstation is positioned in the lithographic apparatus, it may be necessaryfor engineering issues to remove the substrate/object from the substratetable for drying by the active drying station ADS.

Another immersion lithography solution which has been proposed is toprovide the liquid supply system with a seal member which extends alongat least a part of a boundary of the space between the final element ofthe projection system and the substrate table. The seal member issubstantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis). A seal is formed between the sealmember and the surface of the substrate. In an implementation, the sealis a contactless seal such as a gas seal. Such a system is disclosed in,for example, U.S. patent application Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 8. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European patent application no. 03257072.3, hereby incorporated inits entirety by reference, the idea of a twin or dual stage immersionlithography apparatus is disclosed. Such an apparatus is provided withtwo substrate tables for supporting the substrate. Leveling measurementsare carried out with a substrate table at a first position, withoutimmersion liquid, and exposure is carried out with a substrate table ata second position, where immersion liquid is present. Alternatively, theapparatus can have only one substrate table moving between the first andsecond positions.

Embodiments of the present invention may be applied to any immersionlithography apparatus and any liquid supply system (including relevantparts thereof), in particular, but not exclusively, to any of thoseliquid supply systems mentioned above and the bath of liquid asdescribed above.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1. A lithographic apparatus comprising: an illumination system adaptedto condition a beam of radiation; a support structure configured to holda patterning device, the patterning device configured to impart the beamwith a pattern in its cross-section; a substrate table configured tohold a substrate; a projection system adapted to project the patternedbeam onto a target portion of the substrate; a liquid supply systemconfigured to at least partly fill a space between the projection systemand an object on the substrate table with a liquid; and an active dryingstation configured to actively remove the liquid from the object, thesubstrate table, or both.
 2. An apparatus according to claim 1, whereinthe active drying station is positioned between the projection systemand a substrate post exposure processing module.
 3. An apparatusaccording to claim 1, wherein the substrate table transports the objectto the active drying station.
 4. An apparatus according to claim 1,wherein the substrate table supports the object during active removal ofliquid from the object by the active drying station.
 5. An apparatusaccording to claim 1, wherein the active drying station comprises a gasflow device configured to provide a flow of gas over a surface of theobject, the substrate table, or both.
 6. An apparatus according to claim1, wherein the active drying station comprises a gas inlet configured toprovide gas onto a surface of the object, substrate table, or both. 7.An apparatus according to claim 6, wherein the gas inlet forms a gasknife.
 8. An apparatus according to claim 7, wherein the gas knifefurther comprises a further gas inlet and a gas outlet positionedbetween the gas inlets.
 9. An apparatus according to claim 6, furthercomprising a gas outlet to remove gas from the surface of the object,substrate table, or both, the gas inlet substantially surrounding theperiphery of the gas outlet.
 10. An apparatus according to claim 6,wherein the gas inlet comprises a gas shower with at least ten inlets.11. An apparatus according to claim 1, wherein the liquid is a firstliquid and the active drying station comprises a first liquid dissolvingliquid supply device configured to provide a second liquid, in which thefirst liquid dissolves, to a surface of the object, the substrate table,or both.
 12. An apparatus according to claim 11, wherein the secondliquid is more volatile than the first liquid.
 13. An apparatusaccording to claim 11, wherein the second liquid comprises a ketone oran alcohol.
 14. An apparatus according to claim 1, wherein the activedrying station comprises a gas outlet configured to remove gas, liquid,or both from the surface of the object, substrate table, or both.
 15. Anapparatus according to claim 1, wherein the active drying stationcomprises a spinner configured to spin the object, substrate table, orboth.
 16. An apparatus according to claim 1, wherein the objectcomprises a substrate.
 17. An apparatus according to claim 1, whereinthe object comprises a sensor.
 18. A device manufacturing methodcomprising: providing a liquid between a projection system and an objecton the substrate table; projecting a patterned beam of radiation,through the liquid, onto a target portion of a substrate using theprojection system; and actively removing the liquid from the object, thesubstrate table, or both.
 19. A method according to claim 18, comprisingproviding a flow of gas over a surface of the object, the substratetable, or both.
 20. A method according to claim 19, wherein the flow ofgas forms a gas knife.
 21. A method according to claim 20, wherein thegas knife comprises providing gas at two positions and removing the gasfrom a position between the two positions.
 22. A method according toclaim 19, further comprising removing gas from the surface of theobject, substrate table, or both at a position substantially surroundinga periphery of a position where the gas is provided.
 23. A methodaccording to claim 19, comprising providing the gas using a gas showerwith at least ten inlets.
 24. A method according to claim 18, whereinthe liquid comprises a first liquid, and further providing a dissolvingliquid, in which the first liquid dissolves, to a surface of the object,the substrate table, or both.
 25. A method according to claim 24,wherein the dissolving liquid is more volatile than the first liquid.26. A method according to claim 24, wherein the dissolving liquidcomprises a ketone or an alcohol.
 27. A method according claim 18,comprising removing gas, liquid, or both from the surface of the object,substrate table, or both.
 28. A method according to claim 18, comprisingspinning the object, substrate table, or both.
 29. A method according toclaim 18, wherein the object comprises a substrate.
 30. A methodaccording to claim 18, wherein the object comprises a sensor.